During the processing of certain shellfish and crustacea, including shrimp, crabs, and lobster, as well as squid, a waste product containing bony, hard shell and beak pans is produced. These bony pans contain chitin and are largely disposed of as a waste product, typically in landfills. While this disposal method is commonplace, it is known that the waste has a high biological oxygen demand (BOD) and may contain pathogens harmful to human health such as strains of E. coli, salmonella, cholera, etc. Consequently, such disposal is not optimal, and may prove hazardous, if leachate from the waste seeps from the landfill into underground water supplies that may be used as a source of potable water.
in the past, attempts have been made to utilize waste containing chitin for agricultural purposes, and to extract chitin from the waste for use in medical applications. For example, an abstract of a published Japanese patent application, assigned Publication No. 03-228888, published on Oct. 9, 1991, describes the agricultural use of a mixture of (1) "the living bodies," skins, shells, residues of the processing of crustacea, insecta, and mollusks with (2) humus created by composting, animal wastes, food residues, and fish scrap at 70.degree. C. or above. The abstract uses autotrophic soil bacteria, not heterotrophs such as Actymonyces, in the process. An autotroph is an organism that uses carbon dioxide as the sole carbon source. The soil bacteria are incorporated into the solid compost (72.6% moisture) mixture, along with a supply of air, to produce an organic fermented fertilizer containing chitosan components. It is alleged that chitosan enhances the stabilization of the fertilizer, causing agglomeration of the soil, thereby elevating water-holding properties and increasing the stability of microelements.
U.S. Pat. No. 5,374,627 relates to a composition containing 1 part by weight of chitosan hydrolyzate, having an average molecular weight in the range of 10,000 to 50,000, obtained by acid hydrolysis or enzymatic hydrolysis of chitosan, and 0.25 to 4 parts by weight of acetic acid, may be used to protect agricultural and horticultural plants from diseases and damage by certain pests. However, it is suggested that this composition may injure the plants. It is further suggested that any possible chemical injury to the plants may be reduced by admixing the composition with a deproteinized juice of alfalfa leaves.
U.S. Pat. No. 5,208,159 relates to the use of strains of chitinolytic bacteria, cultivated at temperatures between 20.degree. C. and 40.degree. C. to prepare a culture material from chitin or chitosan, which is usable directly as a solid antibacterial composition, or which may be fermented at the above mesophilic temperatures to produce such a solid antibacterial composition. Water may be added to the prepared culture material so that it may be used as an antibacterial, antinematode, and plant-cell activating composition.
The utilization of chitin-containing waste as a raw material for purified chitin for use in medical applications is limited relative to the total volume of the waste produced. In the process of producing purified chitin, chitin-containing waste is generally treated with hydrochloric acid to remove calcium and then washed with sodium hydroxide to remove residue or proteinaceous material to produce a semipurified chitin. When this semipurified form of chitin is treated with strong sodium hydroxide solution and heated for several hours, the chitin deacetylates to produce chitosan. This deacetylated form of chitin is useful in certain medical applications, as well as other applications, for example, as a flocculation chemical in waste water treatment.
There is a need for a method of converting chitin-containing waste on a large scale to a useful product to relieve pressure on landfills and to avoid health issues posed by the disposal of a waste containing, or capable of promoting the growth of, pathogenic microorganisms. Preferably, the process should be environmentally friendly, in the sense of not producing byproducts that are potentially hazardous to human health and that would pose a disposal problem. Moreover, process equipment should be relatively inexpensive, and operating costs should be relatively low so that a commercially viable product may be produced.